Preparation And Catalytic Performance Of Chitin Supported Metal Catalysts

Chitin is the second largest natural macromolecule in nature after cellulose.It widely exists in the shell of arthropods and the cell wall of invertebrates.It has been widely studied because of its good biocompatibility,biodegradability,low cost and wide sources.At the same time,chitin molecular chain contains a large number of hydroxyl,acetamide and unique multi-layer micro nano structure,which can have certain dispersion and adsorption effect on metal ions and organic molecules,especially in the field of preparation of functional catalysts,photoelectric energy storage materials,gel film mechanical energy materials and other fields.In this work,chitin nanofiber microspheres were used as carriers to prepare heterogeneous biomass based composite catalysts for catalytic reactions such as efficient hydrogenation of aldehydes,degradation of pollutants and chemical selective hydrogenation,and explore their reaction mechanism,so as to open up a new way for the development and application of new chitin materials.The research results are as follows:（1）Chitin nanofiber microspheres were prepared by the sol-gel strategy using natural chitin as raw material.The supported Pd/Chitin catalyst was prepared as a carrier to achieve the efficient catalytic hydrogenation of aromatic aldehydes to aromatic alcohols.The results show that the abundant hydroxyl and acetylamine groups in chitin promote the high dispersion of Pd nanoparticles,which can be firmly fixed in the catalyst through simple loading and reduction operations.At the same time,the strong interaction between metal and support can effectively improve its catalytic performance.All 15 aromatic aldehyde derivatives showed good substrate applicability.（2）On the basis of chitin nanofiber microspheres,in order to further improve the surface properties and catalytic properties of chitin microspheres.Chitin carbon nanofiber spheres were obtained by calcination.A chitin carbon sphere（NCM）-supported nano palladium catalyst（Pd/NCM）was obtained by impregnation and used for the catalytic degradation of dyes.The results show that the calcined chitin material has significantly increased specific surface area,enhanced conductivity and increased defects,which effectively improve the interaction between metal nanoparticles and carrier materials,and then improve its dye degradation performance.Compared with commercial Pd/C,Nano-Pd,Pd/Chitin and homogeneous Pd（OAC）₂ Catalysts,Pd/NCM shows excellent catalytic activity.It can be reused for 20 times under the condition of low load,and there is almost no activity loss.Moreover,Pd/NCM catalyst can achieve 100%conversion in the degradation of six common dyes.（3）In order to replace noble metal catalysts with non noble metals,a series of transition metal bimetallic Pt-M/Chitin（M:Ni,Fe,Cu,Co,etc.）catalysts were prepared by coimpregnation method with chitin microspheres as carrier,and the selective hydrogenation of 4-nitrostyrene was realized.The results show that Pt-Ni/Chitin catalyst has the best catalytic performance in selective hydrogenation.The characterization results confirmed that the existence of Pt promoted the dispersion of Ni species,the existence of Ni also promoted the improvement of Pt crystallinity,and the bimetallic synergy between Pt and Ni jointly promoted the reaction.The experimental results show that at room temperature,with H₂ as hydrogen source and isopropanol as solvent,100%selective hydrogenation of C=C can be achieved in 3 h,and the yield can reach 99.4%;At 60℃,using Na BH4 as hydrogen source and toluene:H₂O=1:1,NO₂ can be 100%selectively hydrogenated for 3 h,and the yield is as high as 99.9%.At the same time,the rich characteristic functional groups and large specific surface area in chitin molecular chain can maintain high dispersion of bimetals in the preparation and reaction process,and further ensure the catalytic performance of the catalyst.